Trunk piston



Feb 17,1959 w. F. PETERSON ET AL TRUNK PIsToN Filed March 18, l19:57

M E E United States Patent 2,874,010 TRUNKVPISTON William F. Peterson, Creva'Coeiir, 'William .M Venner,

Brentwood, and Percy L. rio'wser, Jr., Iadue, M'o., ias- `sig'nors `to Sterling Aluminum Products, Inc., St. Charles, Mo., a corporation of Missouri Application March 18, 1957, Serial No. 646,719

4'Clllmi. '.(Cl. Soe-13) .This `invention relate's'to trunk pistons, particularly of altype designed for luse'-i'nfiuternal combustion engines fior automobiles. .Such pistons are usually constructed of a metal 'oflrelatively high thermal expansion, such as 'aluminum and v.nuagnesium alloys "containing -va'rious alloying elements 'such as copper, silicon, nickel, -`manganese, etc. Where silicon is employed fon the order Yof 12%, the thermal `I'expansion is materially reduced. Copper, nickel and manganese impart hardness Sand strength to 'the alloy. The temperatures encountered in' internal combustion enginesare,h'owever, high, Vsotliat there'is liability of seizure when hot and of loos'eness when cold.

HA trunk piston of `thefftyp'e described comprises ahead offrelatively 'thicksec'tiom a skirt /of'rela'tive'ly thin section and wrist pin bosses on and insidefofthe skirt. The head is Igrooved Vto receive the packing rings and is'of `smaller diameter'than Vthe "skirt, which latter 'providesthe vguiding crosshead of the piston. The skirt is l'separated froni'ithe head :in one or ybothregions fof the'thrust faces byone'or two circumferential slots, `and 'one 'or `tvvo vertical slots may also be provided. The skirt may -be'of circular 'contour, or oval .with the major-diameter in the regions of the thrust faces. The -skirt is usually given a standard taper with asmaller diameter at the itop.

InPatent No. 2,780,505, issuedto-*applicants assignee, a control ring of `a metal :of relatively low `thermal expansion extends entirely aroun'dithe 'skirtat the' topthereof, which skirt is .separated 'from Athe -head in one yor both thrust.faces. filiat'cont'rol ring is cast-anchored'inithe boss regions, lbutis unanchored in oneor both thrust-'faces by exposing -.the inner part of the controlfring. However, such ,cast-anchoring is 'accomplished' by continuing the envelopme'nt :of the "control ring' by the psto'n-metalextensivelyrinto the separated Lthrusrfaee tor faces. v

One of 'the objects 'of'this invention fisto 'simplify the construction of the Lpiston ydescribed -in lthe patent 'and'to secure .1an .improved m'ode lfof fopera'tion Sand 'an f improved control ofthe :expansion ofthe skirt.

Further'o'bjects 'will appear'from the 'detailed descrP' i tionyin which will 'be 'set'out fan illustrative embodiment of this invention; it is 'tobe understood howeverjthat this invention iissusceptible .of -various 'embodimentswithin the 'scope 'flthe 'appended claims.

A.Referring to thefaccompauying drawing:

Pig. 1 is `a vertical fse'ction on lthe wrist'pin 'axisof a pistonienibodyingthisinvetltion; i

zFig. -3 Ais a section -on vthe lines 3-4-3, Fig. V2;

Pig. 4 is aview similarto FigZ, 'bu'tish'owingfthe 'r'nld and lcore 'in and overwhich the pistonisjcast; y

:Fig 5 fis ase'ction Son 'the 'line 'of Fig. `2,"but showing the mold-and core 1andluiithftlie core expanded;

iFg. "6 isfaview lsimilar to Fig. 5, jbut 'showingthe core collapsed; and Y Fig. 7is a cross-sectionfof the icontrol ring. Generally vstated, 'and in :accordance withran illustrative enbodimenrof thisinventiomthe control fring comprises i a a iirst sector or sectors partially'exposed internally along a thrust facecrfaces and unanchored therein, and second sectors displaced -circumferentially from the rst sectors and cast-anchored 'along the boss regions. However, the cross-sections of thesecondsectors lare of greater rigidity radiallythan the cross-section of the 'irst sector or sectors, the second sectors 'being proportioned as to their crosssections land-length in accordance with the desired radial stress or stresses to =be imparted to the lirst sector or sectors and the piston metal thereover.

vReferring tothe 4accompanying drawing, and more particularly toFigs. l, v2 and 3,11 designates the head'and -2 the Askirt of a lpistonembodying this invention. The head, which is of relatively heavy section, isprovided with packing .ring grooves 3, while the skirt is provided with inwardly extending wrist-pin bosses 4, which are connected to the'head by the pi1lars.5,andwith balancing-lugs 6. The head .is separated from the skirt by one or two circumferential bslots '7, in the region-or regions of the thrust face or 'faces and, in this embodiment, those slots are in the region of the lowest packing ring -groove 3. One or more vertical slots '8 may be provided `in one or both lthrust faces. t Y A control ring 9, 10, Figs. 3 and 7, of ametal of relatively low thermal' expansion, such as cold -rolled steel-or one Tof the low-expansion alloys used 'in,pistons, is inu corporated yin the piston.y This ring comprises sectors .9 which are enveloped -by the piston metal and -castanchored in the boss regions, Fig. 1, and sectors 10 which are only partially enveloped Aby the piston metal in the thrust face regions, Fig. f2.. As described in Patent No. 2,780,505, and hereafter briefed, the control ring 9, 10 when-incorporated inthe piston operatesto stress the sectors 10 andthe piston metal thereover radially outwardly. In 4order 'to control such 'radial 'stress as desired, the rigidity of the control ring sectors@` is vradially greater than that of the sectors 10, as by making the depths of the sectors 9 radially greater thanthose of they sectors 10. In theeem-b'odiment shown in the drawing Figs. 1, 2 and 3, the cross-sections of sectors 10 arefcircular while 'thec'rosssections of sectors IStare `generally rectangular, with .their greater vdimensions extending radially .of the piston.' The entire control ring -m'ayfbefintegraL -or the sectors'may'b'e joined by weldingforrbrazin'g, or they-may be :separate Aand placed together in sa mold and around a core.

As 'an example, -a-,piston of an laluminum alloy, 90% Al, 9,5% Cu, 0,5% `Mg,"having a 'diameter of "4 inches', alength 'of 3.25winches fand proportioned as shown in thefdrawing, :which is toscale, with a control 'ring kof coldirolled steel, the sectors 10 each having a diameter between :0.120 yand0.1.30 inch' and extending Aon an arc between 60 "and 70"., and with the vsectors 9 leach b'etween 0.f190and .0.200 inch wide ',(radiallyo'f ythe piston) and Vbetween 0:060 and 0;070 inch thick, vand "enveloped by v4the piston metal vtoA the lextent shown, vcontrolled `the piston .diameter 'with a :clearance of Aa ffew thousandths of "aninch in #serviceinanfinternal combustion engine. The control ring is positioned in the piston as shown', with the middle parts 'of the sectors F9 enveloped and cast-anchored in the par-ts'S inrtheiregions of the "wrist pin rbosses. The sectorslll fare unanchored -'in Athe thrust -faces. :Howe-ver, instead `of continuing the :enveL opment i' of fthe sectors39 liuto fthe vvthrustfaces as in `Patent No.' 12,780,505, While thefsectors arie Vcontinued "beyond the pillars 4th'eyare left exposed inwardly so as At'o'fbe unanchored 'beyond Ith'elpillars 5. Ac'ontiuuou'sv ferrous alloy in the regions of the bosses, viz., in the pillars 5 but this envelopment extends partially into the thrust face regions,'viz. along 32 andV 33.

Referring now to Figs. 4-6, which illustrate a mold and core for making a piston, which may generallyl be that as shown in Patent Nos.. 2,129,351, 2,676,371 and 2,676,372, designates the outside mold, which is usually in sections sliding on a base and which is provided with cores 21 to form the holes for the Wrist pin bosses. The core is a live-part core, comprising a three-part middle core consisting of parts 22, 23 and 24 and side cores 25, which latter form the wrist pin bosses. Core parts 23 and 24 are provided with arcuate recesses 26 in the regions of the thrust faces to receive the sectors 9,- and the recesses 26 are continued into the core parts 25 at 28, 30 and 31 to receive the sectors 10 and 9 respectively. The recesses 30 are increased axially of the piston at 31 to form ledges 32 and 33 above and radially below the sectors 9, but with the inside edges of the sectors 9 exposed inside ot the piston as shown in Fig. 2. Accordingly, the sectors 9 while wholly enveloped by the piston metal in the pillars 5 and therefore cast-anchored therein, the inside edges of those sectors are exposed so as to be unanchored beyond the pillars. The core parts 23 and 24 are extended upwardly at 35 along the sectors 10 and the recesses 31 are extended upwardly, as shown at 34, Fig. 4, along the thrust faces to the tops of the to-beformed slots 7 and radially outwardly slightly beyond the bottom of the lowest ring groove. The core part 24 may also be provided with a rib 27 to form the vertical slot 8, and where such vertical slot is in both thrust faces the Vgroove 3. Accordingly, when this ring groove is cut, the

circumferential slots 7 will be formed separating the skirt lfrom the head to the extents of the parts 35 without any extra slotting being required. The construction and arrangement of the core parts 22, 23, 24 and 25, is however, such that they not only form the casting, but that they can be readily withdrawn from the casting.

When the alloy is cast on the piston and has solidified, upon cooling from molten to cold condition, the alloy will shrink much faster than will the steel ring so that the alloy will contract and finally arrive at a condition of tension. In so doing the control ring is placed under compression radially as well as` circumferentially in the condition of the parts shown in full lines, Fig. 3. The effect will be to stress the sectors 19 and the piston metal thereover radially outwardly. The thrust faces are, however, at this time connected with the head. There will be no movement of the piston metal 'along the sectors 9 and 10, because any verticalslot 10 is closed by the core part 27. When now the circumferential slots 7 are cut, in this embodiment by cutting of the lowest packing groove 3, the control ring andthe piston metal thereover will both move outwardly on` the thrust face axis so as to form an oval contour of the piston as shown in dotted lines Fig. 3. It will, of course, be understood that the oval is exaggerated for illustrative purposes, because the actual distortion is small. The

' piston-is now machined to size with the skirt of the core part 23 is also provided wtih such a rib. This rib usual round or oval contour. The piston will, however, remain round or oval (slightly) until in use in the engine; until then, the piston metal will remain under tension, While the ring will remain under compression.

In `accordance Vwith the illustrative embodiment of this invention, the sectors 9 'are made of greater rigidity radially than the rigidity of the sectors 1t), and the extensions of the sectors 9 beyond the enveloping piston metal along 5 are proportioned as to their length and cross-section in accordance with the radial outward 26, 28, 30, 31 and 40 therein while the core is collapsed,

Fig. 6, so that when the core is expanded, Fig. 5, the ring will lie within the recesses. The mold sections are now closed and the alloy is cast. After the casting has solidied, core part 22 is retracted so as to permit the core parts 23 and 24 to move into-the space vacated by the core part 22 and so as to clear the ring 9, 10 and also the vertical slot or slots 8. The core parts 23 and 24 are now also moved in radially and retracted so as to permit the side cores 25 to move into the space vacated by the core parts .22, 23 and 24, Fig. 6, in order to clear the wrist pin bosses. This movement of the side cores 25 will also free them from the ring 9, 10 Vbecause the circumferential extensions of the recesses 26, 30, 31 in the side core parts are su'icient to permit such freeing, because the chords of the side cores are smaller than the respective chordal dimensions ofthe casting. The mold is now opened to releasethe cores 21 and the casting can be picked oi.

In the complete casting the control ring will lie within and extend completely around the top of the skirt and will be surrounded by the alloy in the pillars 5 in the regions of the bosses; however, the inner part of the ring is exposed extensively circumferentially and radially along the thrust face region or regions. The continuation of stress to be imparted to the sectors 10 and the piston metal thereover along the thrust faces.

A piston of the character described and made as described can be made with a very low clearance and it will maintain a very close t when either hot or cold. That is for the following reason: As the piston heats up, the head will, of course, expand radially in all directions. Such radial expansion of the head will, however, only be transmitted to the skirt in the region of the bosses. That will tend to relieve some of the strain along the wrist pin axis so that the control ring and the piston metal thereover will move out along that axis. That will cause the ring to tend to return to its original (viz., round or oval) form. In so doing, the strain in the! alloy at the thrust faces is also relieved so as to move in with the control ring at those faces. The piston, even one of an aluminum alloy, will, therefore, remain conformed to the cylinder with a very low clearance.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

the sectors 9 of greaterv rigidity radially than that of the piston metal but partially exposed radially inwardly along an extended part of the separated thrust face so as to leave said rst sector unanchored in said separated thrust face, said ring having second sectors displaced from said first sector, said second sectors being castenveloped for extended distances therealong by the piston y. metal in the :boss regions so as to cast anchor said second sectors therein, adapted to stress said rst sector andthe piston metal thereover radially outwardly, thev cross-sections of said second sectors being of greater rigidity and depths radially than the cross-section of saidv lirst sector and the second sectors being proportioned as to their cross-sections and lengths in accordance with the desired radial stress to be imparted to said lirst sector and the piston metal thereover.

2. A trunk piston of a metal of relatively high thermal expansion, comprising, a head, a skirt provided with wrist pin bosses and thrust faces both of which are axially separated from the head, and a ring of a metal of relatively low thermal expansion lying within and extending completely around the top of the skirt, said ring having first sectors partially enveloped radially outwardly by the piston metal but partially exposed radially inwardly along extended parts of the separated thrust faces so as to leave said first sectors unanchored in said separated thrust faces, said ring having second sectors displaced from said first sectors, said second sectors being castenveloped for extended distances therealong by the piston metal in the boss regions so as to cast anchor said second sectors therein, adapted to stress said first sectors and the piston metal thereover radially outwardly, the crosssections of said second sectors being of greater rigidity and depths radially than the cross-sections of said first sectors and the second sectors being proportioned as to their cross-sections and lengths in accordance with the desired radial stress to be imparted to said first sectors and the piston metal thereover.

3. A trunk piston of a metal of relatively high thermal expansion, comprising, a head, a skirt provided with wrist pin bosses and thrust faces one of which is axially separated from the head, and a ring of a metal of relatively low thermal expansion lying within and extending completely around the top of the skirt, said ring having a first sector of circular cross-section partially enveloped radially outwardly by the piston metal but partially exposed radially inwardly along an extended part of the separated thrust face so as to leave said first sector unanchored in said separated thrust face, said ring having second sectors of general rectangular cross-section with their greater dimensions extending radially and said second sectors being displaced circumferentially from said rst sector, said second sectors being cast-enveloped for extended distances therealong by the piston metal in the boss regions so as to cast anchor said second sectors therein, adapted to stress said lirst sector and the piston metal thereover radially outwardly, the cross-sections of said second sectors being of greater rigidity and depths radially than the cross-section of said first sector and the second sectors being proportioned as to their crosssections and lengths in accordance with the desired radial stress to be imparted to said iirst sector and the piston metal thereover.

4. A trunk piston of a metal of relatively high thermal expansion, comprising, a head, a skirt provided with wrist pin bosses and thrust faces both of which are axially separated from the head, and a ring of a metal of relatively low thermal expansion lying within and extending completely around the top of the skirt, said ring having rst sectors of circular cross-section partially enveloped radially outwardly by the piston metal but partially exposed radially inwardly along extended parts of the separated thrust faces so as to leave said rst sectors unanchored in said separated thrust faces, said ring having second sectors of general rectangular cross-y section with their greater dimensions extending radially and said second sectors being displaced circumferentially from said irst sectors, said second sectors being castenveloped for extended distances therealong by the piston metal in the boss regions so as to cast anchor said second sectors therein, adapted to stress said first sectors and the piston metal thereover radially outwardly, the cross-sections of said second sectors being of greater rigidity and depths radially than the cross-sections of said rst sectors and the second sectors being propor` tioned as to their cross-sections and lengths in accordance with the desired radial stress to be imparted to said rst sectors and the piston metal thereover.

References Cited in the ile of this patent UNITED STATES PATENTS 

